From the cases that I've heard about, only customs sends love letters. For very small amounts, domestic mail may seize the package and not say anything at all. For intermediate amounts, the cops might knock on your door and ask you about the package, but they won't wait around to do a controlled delivery (it's hard to do on regular mail because you don't have to sign for it and can let it sit in the mail box for days). As an example, I know someone who had 30 percocets mailed to him. I guess this is an "intermediate" amount of drugs. He used a fake name and when the cops came, he claimed it was a former roommate who got "weird packages" all the time, but the roommate had moved out days earlier and he didn't know how to contact the guy. Sure it was a bullshit story and the cops may have known it was a bullshit story, but they couldn't disprove him, and the amount of drugs wasn't worth further investigation. Now if it had been 500 percocets, yeah, they would have done a controlled delivery and waited for him to pick up the package, no matter how long that took.